The present invention relates pallet container having an inner plastic container suitable for transporting flowable or liquid substances. In particular, the invention relates to a support structure arranged to enclose and contact the side walls of the inner container. Such pallet containers are particularly useful in the storage and transportation of fluids, for example in the chemical, petroleum or food industry.
A conventional pallet container of the present type is disclosed in the German Patent DE-C 195 11 723. The support structure enclosing the inner container comprises a grid of vertical and horizontal metal tubes, which are deformed at their intersection so as to form four contact points at which the tubes are welded to one another.
In practice, the grid support structure of such pallet containers are subject to various mechanical loads, for example a vertical load when such containers are stacked on one another. In addition, during handling and transportation, the containers may slide and hit one another or may even be dropped causing high impact loading. Such loading of the grid construction, especially at the welded tube intersections can cause breakage of the welds. In addition, with repeated mechanical stress loading at the welds, fatigue cracks can arise in the metal tube material adjacent the tube intersection.
The object of the present invention is to provide a pallet container with an improved connection of the grid elements which allows improved mechanical strength and durability and which allows simple and inexpensive construction of the container.
According to the present invention, the inner plastic container for transporting liquids is supported by a grid structure arranged to enclose and contact the side walls of the inner container. The grid of the support structure comprises first and second elongate elements crossing one another at intersections. Each first elongate element is provided with a receiving opening through which the respective second elongate element passes and penetrates through the first element. The first and second elements are connected to one another at one or more positions in the region of intersection.
Preferably, the inner dimension of the receiving opening of the first opening is dimensioned with respect to an outer dimension of the second element so as to provide a frictional fit of the two elements. In this case, the mechanical strength of the interconnection against bending moments in the plane of the grid is increased.
The outer surface of the second smaller dimensioned elements define two planes of the grid which are parallel to one another. In a preferred embodiment, the first and second elongated elements are connected to one another at these two tangential planes. Normally, the positions will be where the outer surface of the second element lies opposed to the inner surface of the larger dimensioned first element.
In another embodiments the first elongate element is formed to have a tubular profile and is provided with one or more ridges formed along its interior. These inner ridges are arranged to contact the outer surface of the second element when penetrated through the receiving opening. The contact of one or more such ridges with the outer surface of the second element provides the positions at which the elements can be connected. The use of inner ridges of this embodiment adds mechanical strength by reinforcement to the first elongate element and improves the reliability and durability of the connection at the intersection.
The first and second elements used in constructing the grid support structure of the present pallet container can be of various types. The two elongate elements may be solid or hollow or may have an open profile such as a U-shaped or C-shaped profile with an open longitudinal portion. Preferably, both of the elements are metal tubes having a cross-section which may be circular, oval, square, triangular or rectangular. Alternatively, the second elongate element can be provided in the form of a plate which passes through a corresponding slot or hole in the first element. When the two elements are made of metal tubing, the connection at their contact positions is preferably formed by resistance welding. Alternatively, the two elements could be appropriately deformed within their region of intersection so as to produce a form fit connection therebetween. It is also contemplated that the two elements can be made of a high strength plastic material, in which case, the connection can be accomplished by melt fusion bonding or melt adhesive bonding.
The support grid structure of the present pallet container will normally having the first and second elongate elements disposed vertically and horizontally with respect to one another. Preferably, the first elements having the receiving hole will be the vertical elements, while the horizontal elements will penetrate therethrough. Conversely, it is also possible to have the first elongate elements disposed horizontally, while the second elements would be disposed vertically and penetrate through the horizontal elements.
The grid support structure also comprises upper and lower rim elements, which extend about the circumference of the support structure. The upper and lower ends of the vertical elongate elements preferably form a T-intersection with the upper and lower rim elements. The T-intersection is constructed by passing the vertical element into an opening in the rim element, although it does not penetrate through the rim element as do the above grid intersections. The T-intersection can be formed by the same means described above for the grid intersections, with the exception that the vertical elements only pass into a portion of the interior of the rim elements.